1. Field of the Invention
This invention generally relates to integrated circuit and display fabrication and, more particularly, to a carbon nanotube field emission device, with ZnO asperities formed on the nanotubes.
2. Description of the Related Art
Due to their high conductivity and extreme tip sharpness, carbon nanotubes (CNTs) are known to be effective field emitters. The electrical properties CNTs promote high current densities, and the shape of the tube encourages a concentration of electric field lines, enabling the emission of electrons at low fields. The enhancement factor of a field emitter, or how much more easily than a planar surface it emits charge, is based on the geometry of the tip.
Methods for improving the field emission properties of nanotubes have tended to focus on the growth methods, to improve nanotube morphology, or isolation of single walled tubes. Among these are Dong et al. who tested various growth catalysts and Sveningsson et al., who achieved enhanced emission from thorn-like growths at the tips of long CNTs using Fe catalyzed decomposition of acetylene at 700° C.
The field enhancement factor, γ, is a measure of how easily a structure can emit electrons. As described by Dong et al., it as the ratio of the local field at the tip, to the applied field, and for a given material work function is related to the geometrical shape of the tip. It is defined as F=gV/d, where F is the local field on the tip of the tube, d is the distance between the two electrodes, and V is the applied voltage.
Recently, Bannerjee et al. and Jo et al. have described a technique to improve the field emission properties of ZnO nanowires. ZnO nanowires have also been identified as excellent field emitters, though not as good as CNTs. Their method involves growing ZnO nanowires on a carbon cloth. ZnO nanowires are grown via a vapor solid transport method that involves carbothermal reduction of ZnO by graphite powder at 1100° C. The carbon cloth consists of ˜10 μm diameter carbon fibers. They conclude that the improvement of the ZnO field enhancement factor is due substantially to the unique high aspect ratio substrate, i.e. the ZnO enhancement factor is amplified by the high intrinsic high field enhancement factor of the underlying carbon fibers.
Nanotubes have found application in field emission flat panel displays, in which nanotube emitters are used to stimulate individual pixels. Other potential applications include field emission-based electronic, photonic, and sensing devices, cold cathode lighting sources, electron microscope sources. Any improvement of the enhancement factor of nanotubes would lead to an increase in the operating efficiency of these applications, and may open up new applications.